2Samples AISI-SAE 1018 – 0.18 % C AISI-SAE 1045 – 0.45 % C Austenitized at 870°C for 2 hours
3Heat Treatments A – Furnace Annealed – Slow cooled N - Normalized - Air cooled.O - Oil QuenchedWQ – Water quenched.WT(370)– Water quenched, tempered at 370°C for 1 hour.WT(705)– Water quenched, tempered at 705°C for 1 hour.
4Jominy TestGenerally, the faster steel cools, the harder it will be. The Jominy bar measures the hardenbility of a steelSoftestHardest
5Proceed to Furnace Room to: Quench the samples (except the normalized ones)Place the tempering samples into FurnacesJominy Test demonstration
6Pearlite FormationAustenite precipitates Fe3C at Eutectoid Transformation Temperature (727°C).When slow cooled, this is Pearlite (looks like Mother of Pearl)
14Full TTT DiagramThe complete TTT diagram for an iron-carbon alloy of eutectoid composition.A: austeniteB: bainiteM: martensiteP: pearlite
15So What’s a CCT Diagram?Phase Transformations and Production of Microconstituents takes TIME.Higher Temperature = Less Time.If you don’t hold at one temperature and allow time to change, you are “Continuously Cooling”.Therefore, a CCT diagram’s transition lines will be different than a TTT diagram.
16Slow CoolingTime in region indicates amount of microconstituent!
17Medium CoolingCooling Rate, R, is Change in Temp / Time °C/s
18Fast CoolingThis steel is very hardenable… 100% Martensite in ~ 1 minute of cooling!
19What is Tempering?Martensite needs to be tempered to get better ductility. This happens when Fe3C is allowed to precipitate from the supercooled Martensite.
20SpheroiditeIf tempered for a long time, Fe3C forms “spheres” and grows inside Ferrite.Very soft, easy to machine
21Tempering Demonstration Observe Steel Wire Experiment…What causes wire to sag on heating?When cooling, wire gets tight, then sags again. Why?Why does steel snap like chalk when cooled fast, but tempering restores “strength”?
22So What is “Hardenability”? Jominy Bar used to show how cooling rate affects hardnessAlloyed steels (Cr, Mo, Ni, etc.) have higher hardenbility at same cooling rates than carbon steels
23Typical Jomminy Curves 4340: Very hardenable, More expensive1040: Less hardenable, Less expensive
24Go Obtain Tempered Samples Why can we quench the tempered samples (at 705 and 370°C) in water? Will new Martensite form?Grind oxide scale before measuring hardnessConvert data to DPHTurn datasheet to TA